Signal coupling system



SIGNAL COUPLING SYSTEM Filed April 28, 1955 Aw MN wwbw Theodore Unite SIGNAL COUPLING SYSTEM Theodore A. Byles, Villa Park, 11]., assignor to Motorola, Inc., Chicago, 111., a corporation of Illinois This invention relates to signal coupling systems and more particularly to circuits for applying audio signals to one or more loudspeakers.

There are various occasions when it is desirable that audio signals be head in two places. For example, in radio installation in vehicles, or perhaps in the home, loudspeakers may be located so that persons in different areas receive the same audio material. A very common use of two loudspeakers is in the present-day automobiles where a speaker is generally provided adjacent to the dashboard for the use of those in the front seat and a second speaker is often installed for the benefit of passengers in the rear seat. Of course, it will be appreciated that not all installations are made with two speakers and that it would be advantageous to have apparatus to which a second speaker could be added Without requiring complicated circuit changes. Furthermore, it should be apparent that provision for adjustment of the relative volume delivered by each speaker is desirable so that if different listening conditions exist at the two speaker 10- cations, compensation may be made through appropriate variation in the relative outputs of the devices.

States Patent Accordingly, it is an object of this invention to provide an audio signal coupling system of inexpensive construction which applies signals to a local speaker and permits rapid and convenient conversion to incorporate a remote speaker in the system.

A further object is to provide an audio signal coupling system which may supply signals to one or two loudspeakers and wherein the relative output volume of the speakers may be easily regulated through an adjustable provision which is rendered ineffective when only one speaker is employed.

A feature of the invention is the provision of an improved audio signal coupling system including a multicircuit connector having contacts which may be bridged for single speaker operation and which may be coupled to an additional speaker by connection to the multicircuit connector.

Another feature of the invention is the provision of an improved audio frequency signal coupling system for selectively connecting one or more speakers, and including a balancing volume control bridged across the speakers in the system for regulating relative signal input to each speaker. The system also has connector'apparatus arranged to disable the balancing volume control when a single speaker is employed with the other speaker disconnected. 7

Further objects, features and advantages of the invention may be seen upon consideration of the following :description when taken in conjunction with the drawing,

bl'o'ckiformt This invention provides an audio signal coupling system for automobile radios, and the like, with which it is often desired to employ a second or remote loudspeaker. The system includes a circuit coupler accessible from the outside of the receiver enclosure which may be bridged by a suitable connector in order to complete the circuit for a local or first loudspeaker. By simply substituting a connector for the original bridge, a remote or second loudspeaker is connected to the circuit coupler so that both speakers are operative. In so adding the second loudspeaker a variable volume balancer is also shunted across each speaker so that the relative signal input to each may be altered thus accounting for different listening conditions at the speaker locations. This volume balancer is automatically rendered ineffective when the local speaker is used alone in order to prevent power loss therein, and so that it may not usurp the function of the regular volume control provided in the receiver circuit in known manner.

Referring now to Fig. 1 there is shown the interior of an automobile 10 on the dashboard 12 of which there is installed a radio receiver 15. Control knobs 16 and 17 are used for appropriate adjustment of the receiver. An antenna 20 may also be provided and a local loudspeaker 22 is shown on the dashboard primarily for the benefit of persons in the front seat of the automobile. A remote loudspeaker 25 may be installed adjacent the rear seat for the benefit of persons sitting there or to supplement the speaker 22. A suitable connector line 27 is shown extending between speaker 25 and the receiver 15.

A more detailed description of the circuit will now be given in connection with the diagram of Fig. 2. Here it may be seen that the antenna 20 is connected to radio frequency amplifier stage 30 in the receiver 15. Stage 30 is further serially connected to converter stage 32, intermediate frequency amplifier stage 34 and detector stage 36. These respective stages may be of standard design and provide a superheterodyne radio receiver circuit in which radio signals may be selected, amplified and demodulated. A variable resistor or volume control 37 is shown connected to the detector stage 36 and this control provides variation of the level of the signal applied to audio frequency amplifier stage 38. Stage 38 provides amplification of the demodulated signal and applies the signal to the primary winding of output transformer 40.

The secondary of transformer 40 is connected to the common return or ground and to the voice coil of local loudspeaker 22. The other side of this voice coil is connected to terminal 41 of connector strip 47 which is available from the outside of the enclosure of the receiver 15. Terminals 42 and 43 of connector strip 47 are respectively connected to the variable arm of potentiometer or variable resistor 48 and to one end of this resistor. The other end of resistor 48 is connected to the junction of the secondary winding of transformer 40 and one side of the voice coil of speaker 22. Terminal 44 of strip 47 is connected to ground.

Jumper wire 50 is adapted to electrically connect terminals 41 and 44 of the connector strip 47 which would couple together the secondary winding of transformer 40 and the voice coil of speaker 22. In this condition, therefore, the radio receiver 15 would apply signals to speaker 22 the signals from which would be reproduced by speaker 22. It may be observed that at such time variable resistor 48 is ineffective in the system since only one terminal thereof is. connected. The regulation of the volume would be obtained in conventional manner by varying resistor 37.

Assuming now that it is desired to add a second or remote loudspeaker to the system, it is only necessary to r m v i w e a d. in a in a s t 9 1- 7 3 nector plug 52. The voice coil of remote speaker 25 is connected by means of line 27 across a pair of interconnected terminals of plug 52 which join terminals 41, 42

and :a second pair ofiinterconnectedterminals which elecitrrcally join terminals 43,44. Therefore the voice coils .of speakers 22 :and 25 would be in series across the secondary winding .of transformer 40 so that both of these speakers reproduce-the signals applied thereto. Further more, the arm of variable resistor 48 is connected to the cornmon'juriction of the voice coils of speakers 22, 25 and the end terminals of this resistor are bridged across both speakers. Accordingly by adjustment of resistor 438 either speaker may be short circuited so that it receives no signal, or the arm may be set at an intermediate position giv- =ing any desired relative balance of input to the speakers.

Thus if the listening conditions differ at the locations of the speakers, a desired balance of volume may be obtainedby the adjustment of resistor 48. Such adjustment might be desirable if the surrounding noise level differs at the two locations or if persons in either of the locations do not desire signals of equal volume. As mentioned, this may even be carried to the point of completely silencing one of the-speakers.

The variable arm of resistor 48 may be'mounted so as to be adjustable by one of the knobs l617 or even mounted concentrically with the adjustment knob ofsome other control of the receiver. It should be pointed out that adjustment of resistor 48 only regulates the relative output of the speakers and that the total volume may be adjusted by appropriate settings of resistor 37.

This invention provides therefore a signal coupling system through which a remote loudspeaker may be quick ly and conveniently added by the simple change of a connector available externally of the receiver housing. It is only necessary to remove jumper wire 50 and install the'plug 52 in its stead. When only the single local speaker is used resistor 48 is ineffective in the circuit so that there is no power loss therein and so that the settings of its variable arm have no effect on the output of the single loudspeaker. However, when the second speaker is installed the volume balancing provision is automatioally connected into the circuit to provide complete range ofregulation of the relative outputs of the two loudspeakers.

I claim:

1. A-wave signal receiver adapted to be coupled to a remote loudspeaker while loudspeaker includes two conneotors each having-two portions, said receiver including in combination, output circuit means providing an audio Signakconnector means having four terminals adapted to be connected to the connectors of the remote loudspeaker, a local loudspeaker series connected with said output circuit means and first and second terminals of said connector means, potentiometer means having an end terminal coupled to said local loudspeaker and a second end terminal and a movable terminal connected to the third and fourth terminals of said connector means respectively, and a jumper connector adapted to be connected to said first and second terminals to complete a circuit through said local loudspeaker, said jumper connector being removable from said connector means for connection thereto of the connectors of the remote loudspeaker, with the portion of one connector being connected to said first and fourth terminals and the portions of the other connectors beingconnected to said second and third ter- 2. A wave signal receiver adapted to be coupled to a second loudspeaker which is connected across first and second pairs of coupling means, said receiver including -in combination'audio output circuit means providing an audio' signal, connector means available'externally of the receiver and having a plurality of terminals, -said conconnected with said output means and said first and secnector means being adapted to be joined to the coupling means, a local loudspeaker series connected with said output circuit means and first and second terminals of said connector means, variable resistor means having a portion coupled to said local loudspeaker and further portions coupled across third and fourth terminals of said connector means, and jumper circuit means fitted to said first and second terminals to complete a circuit to said local loudspeaker, said jumper circuit means being removable from said connector means for replacement by the coupling means, with pairs -of terminals of the coupling means connected to said first and second terminals and said third and fourth terminals respectively of said connector means, whereby said variable resistor means is operable to balance signals between said local loudspeaker and the second loudspeaker.

3. An audio frequency signal system including in combination, output means for supplying anaudio signal, first connector means having first, second, third and fourth terminals, a local loudspeaker series connected with said output means and said first and second terminals of said first connector means, potentiometer means having rend terminals and a movable tap, one of said end terminals beingconnected .to the common connection between said output means and said local loudspeaker, said movable pling line, said second and fourth terminals of said second connector means being interconnected and being connected to said remote loudspeaker through said coupling line, so that signals are applied through said coupling line to said remote loudspeaker and said potentiometer controls the relative strengths of the signals applied to said local and remote loudspeakers.

4. An audio frequency signal system including in combination, output means for supplying an audio signal, first connector means having first, second, third and fourth terminals, first audio signal transducer means series ond terminal-s of said first connector means, potentiometer means having end terminals and a movable tap, one of said end terminals being connected to the common connection between said output means and said first transducer means and said movable tap and said other end terminal being connected to said third and fourth terminals of said first connector means respectively, .a jumper connector adapted to fit said first connector means for intercoupling said first and second terminals and provide operation of said first signal transducer means, a second audio signal transducer and second connector means having first, second, third and fourth terminals adapted to be connected to the corresponding terminals of said first connector means, said first and third terminals of said secondconnector means being interconnected with each other and being connected to said second signal transducer, said second and fourth terminals of said second connector means being interconnected and being connected to said second signal transducer, so that when said jumper connector is removed and said secondconnector is coupled to said first connector signals are applie'dthrough signals in said first and second transducers.

References Cited in the 'file of this patent UNITED STATES PATENTS 2.573.122 Weber Oct. so, .1951 

